1. Field of the Invention
The present invention relates to a hollow golf club head made of metal, and particularly relates to a golf club head having a shape of a wood type or a shape approximating the shape of the wood type.
2. Description of the Related Art
Hollow metal heads has been used broadly as wood type golf club heads for drivers or fairway woods. Generally, as shown in FIG. 6, a wood type hollow golf club head 1 has a face portion 2 for hitting a ball, a crown portion 3 forming a top surface portion of the golf club head, a sole portion 4 forming a bottom surface portion of the golf club head, a side portion 5 forming toe-side, back-side and heel-side side surface portions of the golf club head, and a hosel portion 6. A shaft 7 is inserted into the hosel portion 6 of the golf club head 1, and fixed thereto by a bonding agent or the like. Incidentally, recently, many golf club heads called utility clubs have been commercially available. Various golf club heads similar to the wood type golf club head (that is, having a face portion, a sole portion, a side portion and a crown portion) have been commercially available as a kind of utility golf club head.
An aluminum alloy, stainless steel or a titanium alloy is used as a metal forming the hollow golf club head. In recent years, particularly a titanium alloy has been used broadly.
Incidentally, the naming of the wood type golf club head is derived from persimmon, which has been used for a long time as a raw material of the wood type golf club head. Golf club heads made of metal have been in poor demand particular for experienced golfers because the sound of hitting a ball is higher-pitched than that with a persimmon head. Various measures have been taken to reduce the shrill sound of hitting a ball. As one of the measures, there is a technique in which a metal sheet is joined to an internal surface of a golf club head at a center of a sole portion (JP-A-Hei.11-347156), and a technique in which a metal sheet is spot-welded to the internal surface of a golf club head on the heel side of a sole portion, and a gap of 0.02-0.2 mm is formed between the metal sheet and the sole portion (JP-A-2000-254260).
However, along with the popularization of wood type golf club heads made of metal, recently, the metallic shrill sound of hitting a ball peculiar to the wood type golf club heads made of metal is preferred inversely with the previous tendency. That is, the shrill sound of hitting a ball generated when the ball is hit on a sweet spot of a golf club head is preferred as proof of a good shot. Thus, the persimmon-tone sound of hitting a ball is disliked as a sound giving no impression of a short carry of a ball.